Coating of fibrous surfaces



Filed Oct. 5, 1935 COATING OF FIBROUS SURFACES M MN w 5 N. Q 7 v G d M fl my M W n I A ,A .1 a w G 0 0 b5, k V v n-wbmwwl OwmWwwI Q Q 265 N 25.5 v 0 owpwux numb: 6 NM siwhw 2 35 Q .m\ m MN 3 Q w\ 9 n 0 Q "R m\ 0 y W G 0 w \w Q QM.\ mfl r1. K

Se t. 20, 1938.

Patented Sept. 20, 1938 UNITED STATES PATENT OFFICE 2,130,536) ooamo or muons summons John Fletcher, Kenmore, N. Y., a-ssignor to Plastergon Wall Board Company, Bufi'alo, N. Y., a corporation of New York Application October 5, 1935, Serial No. 43,738 11 Claims. (01. 91-40) An object of the invention is to provide an improved method of applying a coating to a fibrous surface or sheet, with which the penetration of the coating material into said surface or sheet will be relatively slight, with which a fibrous surlO face may be coated in a simple, rapid and inexpensive manner, with a minimum of handling of the object to be coated, and with a minimum of manual labor.

Another object of the invention is to provide 15 an improved method of coating a fibrous sheet, such' as paper, with which the coating material will remain largely on the surface of the sheet, with which the finish as to gloss or flatness may be varied within limits, and which may be easily 20 and inexpensively performed.

Another object of the invention is to provide an improved method of coating a travelling paper sheet or web, such as the web leaving the drying rolls or cylinders of a paper making machine, and

25- with which the coating may be applied to the web and hardened in a rapid, simple and inexpensive manner while the web is travelling and then be immediately wound or otherwise disposed 30 A'fu'rther object of the invention is to provide an improved method of coating and coloring a fibrous sheet, such asa paper sheet, with which uniformity in the coating and coloring may be obtained, with which the coatingand coloring 35 may be performed while the sheet is travelling,

and which requires no complicated or elaborate apparatus. I

Another object pf the invention is to provide an 50 paper making machines.

Other objects and advantages will be apparent from the following description of an embodiment of the invention,and the novel features will be particularly pointed-out hereinafter in connec- 55 tion with the appended claims.

improved method of coating paper and similar 40 sheets with 'a water dispersion of coating sub- In the accompanying drawing, I have illustrated diagrammatically an apparatus for applying a water dispersion of coating material to a travelling paper web, as the web leaves the drying cylinders or rolls of a paper making machine 5 in order to illustrate an important embodiment of the invention.

' Lacquer emulsionsor lacquer dispersions in the water phase, have recently been made available for industrial use as also water dispersions of various other coating materials of the type which harden upon the evaporation of a solvent, among "which may be mentioned nitro cellulose lacquers,

synthetic resins, natural fossil resins and rosin. A description of lacquer emulsions or water (115- persions and their preparation, composition and use has recently been published and made available to the trade by The Hercules Powder Company Inc. of Wilmington, Delaware, in a booklet entitled"Lacquer Emulsions, and copyrighted in 1935 by The Hercules Powder Company Inc.

Referring particularly to the drawing, the invention is illustrated as it has been successfully applied to a paper making machine for the coating of the travelling paper web leaving the paper making machine. The travelling web III of freshly formed paper, after passing over a desired nmnber of drying cylinders or rolls II, is conducted over "an idler cylinder I! to the upper end of a. calendering device or unit l3. This calendering device includes a series of floating, calenderin'g cylinders ll, l5, l6, l1, l8 and I9 which are arranged above one another, guided for vertical movement infioating contact with one another, and yieldingiy urged in contact with one another under heavy pressure. Such a calendering device is a common attachment to or a part of paper making machines for calendering the web leaving the drying cylinders.

The web' Ill passes alternately around these 40 calender rolls I to l9, and then passes from the lower cylinder or roll l9 to the top cylinder 20 01' a second calender device or unit 2|. As, the web l0 passes around the calender rolls in the unit IS, the opposite faces of the web are successively moistened by water applied to the cylinders or rolls l5 and II which engage opposite faces of the "web, the application of moisture to these rolls or cylinders being obtained by water boxes 22 and 23, each of which is fitted against a side of a cylinder, with the cylinder forming a side wall of the box, the boxrunning approximately for the full length of the cylinder. This is common practice in the calendering devices of paper making machines.

The second calender. unit 2i includes: in addition to the top cylinder 20, additional cylinders 24, 2|, 2, 2'1 and 28 all-arranged as usual in paper making machines in superposed, floating contact with one another, and under high pressure on one another. The web ll. after passing over the top calender roll 2., passes alternately around the lower rollers 24 to 28 of that unit, and then passes to the top roller 2| of another calender unit II. The web, after passing around the top roller 2| of this third unit 8|, passes alternately around the successive and lower rolls L12, :3, 34 and 35 of that unit, and then is conduc over an idle roller 30 to the winding or cutting mechanism, as usual in paper making machines. These three units it, 2i and 80 thus represent three usual calendering units through which the web is mmonly passed successively inleaving the-drying cylinders before it is wound or otherwise disposed of.

In the unit 2i, two of the rollers or cylinders 25 and 26 intermediate the top and bottom rollers are heated in any suitable manner such as by steam, and similar rollers 32, and 33 in the unit Ill may also be similarly heated. A water box 31 is disposed along the roller 21 which is below the heated rollers 25 and 2| in the intermediate calender unit 2i, so as to apply a liquid coating to the cylinder 21 and through it to one face of the travelling web iii. In this water box 81, of which the cylinder 21 forms one side wall, I place the water dispersion of the coating material, and thus as the cylinder 21 rotates in the direction of the arrow, it will carry some of this coating material with it and transfer it to one face of the' travelling web it. l I

The water-dispersion of the coating material may be prepared in any desired manner and of any desired material, but among such materials which are particularly 'useful in the coating of paper may be mentioned the nitro cellulose lacquers, synthetic resins, natural fossil resins, rosin, particularly the rosin which is the residue from the distillation of turpentine from turpentine sap, and also oil and water soluble termite and fungus resisting materials, as well as water dispersions of insoluble termite and fungus resisting materials. Flmgus and termite resistant materials are well known, and include arsenic compounds, coal tar products and certain zinc salts. Various mixtures of these materials to make up the coating compound, in water dispersion phase, may be used when desired. i

The water dispersion or emulsion of the coating material which is placed in the water box 31, may also contain any desired coloringmaterial, either of the water or oil soluble type. The preferred dyes are-soluble in coal tar solvents, or in solvents which are immiscible with water, or with pigments in suspension, so as to impart to the coatin any desired color.

In the operation-of this coating apparatus, the paper web II which leaves the drying rolls or cylinders ii ofthe papermakingmachineis ofa I Is temperature materially above room temperature, and as it passes through the calendering unit it, the opposite faces of the web are moistened ,by water contained inthe water boxes 22 and 23. At the same time the web is subjected to considerable pressure as it passes between abutting rollers of the unit II. In the making of paper, it is necessary to dry the web quite thoroughly throughout, and then to moisten the faces thereof in order to calender the surfaces of the web.

After being moistened on its faces and subtofore, the web passes through the second unit.

in which the water dispersion of the coating material is placed, and the roller 21 takes up a film of this coating material from the box 31 and carries it into contact with the web ill on one face thereof, excess coating material of the film being squeezed out by the pressure between the rollers 26 and 21 and running back into the box 31. The coated face of the web then passes between the rollers 21 and 28 where it is subjected to pressure to force the coating compound into further contact with the web fibres, and then this coated face is exposed to air as it passes around the roller 2| and travels to the top of the third calender unit As this freshly coated web leaves the roller 21 and passes in contact with the air to the third calendering unit It. a considerable portion or all of the volatile solvent of the coating is driven off by evaporation, it being understood that the freshly coated web in this zone has a temperature above room temperature, and the escape of steam and moisture from the web when so exposed to air aids in carrying oi! the volatile solvent. with the result'that by the time theweb and the moisture in excess of that desired in the finished web is driven off, and a smooth calendering surface is provided on the coated web. The web then passes over the roller 38 to the winding roller or the, cutting machine as usual 7 in paper making machines.

In the foregoing description, it will be understood that the coating may be applied through the water box of the usual calendering mechanism of paper making machines, without any increase in equipment or any additional handling of the web, but if it is desired to coat both faces of the web, an additional calendering unit should preferably be provided, so that the opposite faces of the web may be successively coated and then a'drying and calendering finish given to the web.

It will be understood that the apparatus illustrated diagrammatically in the drawing, and .which constitutes part of a well known paper making machine, maybe modified within the principle of this invention, and the improved method of coating may be applied to flat sheets by performing similar operations on the web, such as, for example, by first moistening the face of the web to be coated, then calendering it, applying a water dispersion of thecoating material thereto, allowing the volatile solvents and part of the moisture to evaporate, and then further calendering or drying the coated sheet.

I have found that by first moistening the web before the water dispersion of the coating material is applied thereto, there is less penetration of the coating material into the fibers of the sheet, also that the heating of the web or sheet before the water dispersion of the coating material is applied is advantageous, in that the heat of the web quickly eliminates the volatile solvent of the coating material in a steam atmosphere, and also part of the moisture of the coating, so that less travel of the web and less exposure of the web to air is required before being further calendered and dried. The driving oil? of the solvent in an atmosphere of steam which occurs while the web is travelling between the. units 2| and tends to produce a mat finish on the web, which is particularly valuable as a primer coat or finish to receive paints, particularly water paints. If a higher gloss on the coatedface of the web is desired, the preliminary moistening of the web before the water disperson of the coating material is applied is eliminated or the amount of preliminary moistening reduced. The preparation of the water dispersion of various substances is now generally understood and is explained in the booklet entitled Lacquer Emulsions hereinbefore referred to. The preparation of such an emulsion may, however, be briefly described as follows:

The first step in preparing a lacquer emulsion is to make up the base lacquer. The composition of this base lacquer depends upon the usesimilar type are available, which probably would give comparable results. The ratio of lacquer phase to water phase vwill ordinarily vary between 2 parts of lacquer to 1 part of water and 3 parts of lacquer to 1 part of water. In general, the lower the percentage of water used in the emulsion, the higher the" viscosity of the finished emulsion will be. In making all emulsions and especially those with a low percentage of water,it is best to use a procedure known as Seeding. By this procedure about a quarter of the lacquer base is first dispersed in the entire water phase and this mixture is passed through the homogenizer to form a dilute emulsion. To this is then added the remaining three-- quarters of the lacquer base and the complete mixture again is emulsified. The size of the emulsion particles is decreased by repeated passes. through the homogenizer. One or two passes is usually sumcient however.

In making up a pigmented lacquer emulsion' on the Manton -Gaulin, the following technique is recommended. The baille ring on the second stage homogenizer should be left out and a properly supported 200-mesh screen placed over the outlet of the second stage homogenizer. All of the water phase should be added first with only a small part of the lacquer phase, and pumped through the machine; the only pressure should be that built up by the resistance of the screen.

- like finish on the coating.

tion of nitro cellulose in solvent. Such a solution dries by evaporation of the solvent, depositing a uniform continuous film, and with the addition of resin a glossy film. A flocculation of the solids-occurs on the coated sheet or web when a water phase dispersion of nitro cellulose in solvent is used as the coating material. ,The evaporation of the solvent and the water flocculates the solids and this flocculation deposits on the fibers.

This coating. has a mat-appearance and is particularly suitable for its intended use as a priming or'base coat for finish coats of clear lacqueror nitrocellulose in solvent.

'Nitro cellulose dispersion in the water phase has a milky appearance.

It will be understood that various changes in' the details, materials and steps which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art' within the principle and scope of the invention as'expressed in the appended claims.

I claim as my invention: 1. The method of coating the fibrous surface of a sheet-like object, which comprises pre-wetting said surface with water, applying to the said wet surface a coating of a water dispersion of a nitrocellulose lacquer containing a solvent for the nitrocellulose, then exposing the coated object to a drying, humid atmosphere sufiicient to eliminate the solvent without substantial elimination of the water and deposit the nitrocellulose lacquer solids on said surface, and then drying the object to remove the water.

2'. The improved method of applying a coating to a surface of a fibrous object which comprises moistening the surface of the object with water, applying to the moistened surface a coating of a water dispersion of a nitrocellulose lacquer, drying the coated object until the coating passes the tacky stage, and then further drying and calendering thecoated surface to produce a mat- 3. The improved method of applying a coating, to a surface of a fibrous object which comprises moist'ening the surface of the object with water, heating the object, applying to the moistened and heated surface a coating of a water .dispersion of a'nitrocellulose lacquer, drying the coated ob- Ject until the coating passes the tacky stage, and calendering the partially dried, coated surface to produce a mat-like finish on said coating.

4. The improved method of. coating a paper web which comprises imparting translation to said web, heating and moistening the face of said web to be coated, applying to the heated and moistened face of the moving web a coating of a .water dispersion of a nitrocellulose lacquer, drying the coated webwhile in motion until the coating passes the tacky stage, and then calendering the coated surface with heat to dry the coated web and produce a mat-like finish on the coating.

5. The improved method of coating a surface of a fibrous object which comprises applying to said surface while in'a heated and moist condi-, tion, a coating of a water dispersion of a nitrocellulose lacquer, drying the coated surface until the coating passes the tacky stage, and then calendering the coated surface with heat to further dry the coated web and produce a mat-like finish on the coating.

6. The improved method of coating a paper web which comprises applying to the hot, moist a nitrocellulose lacquer containing a volatile solvent for the nitrocellulose, passing the.- coated web in contact with air to partially eliminate the volatile solvent in said coating and carry the "coating on the surface past approximately the tacky stage, and then calendering and further drying the coated web on the web.

'7. The improved method of coating a paper web which comprises translating said web while heated and moistened on that surface which is to be coated, applying to the moistened and heated surface a water dispersion of a nitrocellulose lacquer, exposing the travelling coated web to a drying action until the coating passes approximately the tacky stage, and then calendering the travelling coated web with heat to harden and dry the coating and produce a mat-like finish thereon.

8. The method of coating a paper sheet which comprises coating a face of the sheet which, before coating, contains substantially more moisture than it will retain in normal atmospheric conditions, with a water dispersion of a nitrocellulose lacquer containing some volatile solvent for the nitrocellulose, and immediately exposing the coated sheet to a drying atmosphere at a temperature above normal room temperature to eliminate the solvent and deposit the lacquer solids on said surface, and then eliminating the remaining water from said deposited coating.

9. The improved method of coating a paper web which comprises applying to the traveling, hot, moist web leaving the drying cylinders of a paper making machine, a coating of a water disto produce a mat finish persion of a nitrocellulose lacquer and containing intermixed therein a termite and fungus resistant material, saiddispersion containing a volatile solvent for the nitrocellulose, then passing the hot coated web immediately in contact with air to partially eliminate the volatile solvent in said coating sufiiciently to quickly carry the coating on the surface past approximately the .tacky stage, and then further drying the coated web.

' 10. The improved method of coating a paper web which comprises continuously app y n to the traveling, hot, moist web leaving the drying cylinders of a paper making machine, a coating of a water dispersion of a nitrocellulose lacquer containing a volatile solvent for the nitrocellulose, then immediately passing the hot coated web in contact with air to quickly and at least partially eliminate the volatile solvent in said coating sumciently to carry the coating on the surface past approximately the tacky stage, and then further drying the coated web.

11. The improved method of applying a coating to a surface of a fibrous object which comprises coating a face of said object which before coating contains substantially more moisture than it will retain under normal atmospheric conditions, and while at--a temperature substantially above normal room temperature, with a water dispersion of a nitrocellulose lacquer containing some volatile solvefitfor the nitrocellulose, then immediately exposing the hot coated sheet to contact-with air to partially eliminate the volatile solvent in said coating sumciently to carry it past approximately the tacky stage, and then further drying the coated object.

- JOHN I'LE'I'CHER. 

